This invention relates to automotive tire parameter monitoring systems. More particularly, this invention relates to a tire parameter sensor unit having a real time tire parameter storage capability for accumulating information relevant to a given tire.
Tire parameter monitoring systems are known and are commonly used to monitor one or more parameters of interest in individual pneumatic tires of a vehicle and to provide an advisory signal to the driver, or an on-board computer system, whenever the monitored parameter in one or more of the vehicle tires reaches a value lying outside of a predetermined safe range. The parameter is typically internal tire pressure, tire temperature, internal tire air temperature, lateral tire force, or some other parameter of interest. The advisory signal is typically generated by an r.f. signal generator/transmitter controlled by a microprocessor connected to the tire parameter sensor(s), the advisory signal being generated whenever the tire parameter measured by a given sensor lies outside a predetermined normal operating range, signifying either a high or a low parameter condition. This r.f. signal is transmitted to a vehicle-mounted receiver, which uses the advisory signal to alert the driver either visually (by activating a warning lamp or display) or audibly (by activating an audible alarm) or both. Electrical power to the sensor unit comprising the parameter sensor(s), the microprocessor, the r.f signal generator/transmitter, and any ancillary circuitry is usually provided by a battery or an inductive power source. The sensor unit components and the power source are typically all mounted on a substrate and encapsulated by a suitable protective material.
Due to concern for automotive safety, and spurred on by increasingly stringent governmental regulations, tire parameter monitoring system technology has advanced to a stage at which a complete sensor unit can be installed in a tire at the point of manufacture by embedding the sensor unit in the tire carcass. Such a sensor unit includes a non-volatile memory in which tire information is stored at the point of manufacture. The stored tire information may include the date of manufacture, tire type, place of manufacture, and tire serial number, and this information is normally stored in read-only form so that it cannot be altered. Once installed, the sensor unit can be interrogated in the future by special purpose interrogator devices to retrieve the stored information usually by using well-known r.f. interrogation techniques. Thus, for example, when a given tire equipped with such a sensor unit fails, or is replaced, the stored and extracted information can be useful in determining tire lifetime, tire failure rate for an identifiable tire manufacturing run, and tire failure rate for a given tire design. Since the sensor unit is physically incorporated into the tire, tampering is virtually impossible without destroying the tire so that the information extracted from a given sensor unit is virtually guaranteed to accurately reflect the origin of the tire to which the sensor unit is attached.
Tire parameter sensor units having the stored tire information capability only carry original point of manufacture information. While useful, this information falls short of providing any information concerning the tire after manufacture, especially information pertaining to the actual use of the tire after it has been manufactured and placed in the stream of commerce.